The present invention relates to semiconductor devices and their manufacture, and more specifically to a structure and method of making a coil inductor on a semiconductor chip, on an interconnection device, or on a plurality of stacked semiconductor chips.
For certain applications it is desirable to provide an inductor having a relatively large inductance value on a microelectronic element such as a semiconductor integrated circuit chip, or on an interconnection element such as an interposer for electrical connection with a microelectronic element in a microelectronic package. A relatively large inductance value is needed when the inductor is used in a power supply voltage regulator, such as a buck voltage regulator commonly used to step up or step down a voltage from one direct current (DC) supply voltage to another. Heretofore, buck voltage regulators have been implemented as devices mounted to a circuit board rather than on microelectronic elements or interconnection elements.
Heretofore, on-chip inductor structures have suffered from insufficient inductance per unit area of the surface of the microelectronic element. It is common for on-chip inductor structures to be formed as a spiral disposed in a plane parallel to a front or a rear planar surface of the chip. The magnetic flux in a spiral inductor extends in a direction perpendicular to the planar surfaces of the chip, making it hard to achieve sufficiently high inductance with a spiral inductor. Moreover, in on-chip inductors, an input end of the inductor can be disposed relatively far from an output end of the inductor, which can reduce the effective inductance.
In light of the foregoing, further improvements can be made to a coil inductor incorporated on a microelectronic element or interconnection element, and to a method of making such inductor.